1. Field of the Invention
The presently disclosed subject matter relates to an image pickup apparatus, and particularly, to an image pickup apparatus configured to adjust automatic focus (phase difference AF) of a phase difference detection system.
2. Description of the Related Art
FIGS. 15A to 15C illustrate relationships between an image lens 1 and an image pickup surface “m”. When a subject is focused, lights a0, b0, and c0 passed through the parts (components) of the imaging lens 1 converge to the image pickup surface m as illustrated in PORTIONS A and B of FIG. 15A, and a focused image Z0 is obtained on the image pickup surface m. When the focus position is in a front focus state compared to the focused state as illustrated in FIG. 15A, lights a1, b1, and c1 passed through the components of the imaging lens 1 converge at the back (right side in PORTION A of FIG. 15B) of the image pickup surface m, and the lights form different images Za1, Zb1, and Zc1 on the image pickup surface m, as illustrated in PORTION B of FIG. 15B. In a back focus state, lights a2, b2, and c2 passed through the components of the imaging lens 1 converge in front (left side in PORTION A of FIG. 15C) of the image pickup surface m, and the lights form different images Za2, Zb2, and Zc2 on the image pickup surface m, as illustrated in PORTION B of FIG. 15C.
Automatic focus for entering the focused state illustrated in FIG. 15A can be controlled by detecting an amount of defocus (amount of displacement of focus) at the front focus state and the back focus state.
Conventionally, to detect the amount of focus, a beam splitter 3 is arranged between the imaging lens 1 and a solid-state image pickup element 2 as illustrated in FIG. 16, and the light divided by the beam splitter 3 enters a sensor 4 for phase difference detection.
However, there is a problem that the size and the cost are disadvantageous if the dedicated sensor 4 is installed and that the light amount entering the solid-state image pickup element 2 is small due to the beam splitter 3.
Therefore, in Japanese Patent No. 2959142, instead of arranging the beam splitter 3 and the AF sensor 4, a dedicated pixel (sensor unit) 6 for phase difference detection is arranged on part of the solid-state image pickup element 5 as illustrated in FIG. 17 to perform phase difference AF.
More specifically, an image pickup apparatus described in Japanese Patent No. 2959142 relatively displaces the positions between elements in a preset predetermined range of the solid-state image pickup element 5 and lenses (microlenses) arranged above the elements and detects the focused state based on the comparison result of output signals of elements displaced in one direction and output signals of elements displaced in another direction.